The result means Motherwell sit in third and trail Aberdeen by four points with three games to go.

It was a third straight win for United over Well, who have now not beaten the Tannadice outfit in their four meetings this season.

Dow (left) scored United's fourth goal in their rout of Motherwell

Although Motherwell were boosted by the return of Keith Lasley, Stevie Hammell was captain for the day, but it would turn out to be a disappointing day for the Well stalwart as he made his 500th appearance for the club.

A win for Motherwell would have virtually guaranteed at least a third-place finish and European football again next season.

But it was the home side who looked inspired following a minutes' applause for United club legend Frank Kopel, who died earlier this month.

Following great play from Armstrong, the classy midfielder jinking away from his Motherwell markers to set up the opening goal.

His accurate through ball found the feet of Ciftci, who turned inside at the edge of the box before firing home a terrific shot into the top corner.

The class of Ciftci was soon to the fore again and, in an almost carbon copy move to that which led to the first goal, the Turkish striker collected a pass from Armstrong, but this time Motherwell goalkeeper Gunnar Nielsen pulled off a fine save.

Soon after, the Faroese international had to dive low to save a fierce shot from Gary Mackay-Steven as United continued to dominate.

Just before half-time it was 2-0 to United when another swift attack completely outflanked the Motherwell defence.

Armstrong flashed in a cross and there was Ciftci again with goal number 17 for the season to put United in complete control.

Clearly unhappy with the first-half showing, Motherwell manager Stuart McCall made two changes at the break with Henri Anier and Fraser Kerr making way for Ainsworth and Craig Moore.

It certainly helped give the Steelmen some much needed impetus and Lasley should have pulled a goal back for Motherwell, but he blazed a shot high over the bar from only eight yards out.

However, on the hour mark, United sealed this match with a goal of sublime quality.

A header on the half-way line from Ciftci found Ryan Dow, who back-heeled perfectly into the path of Armstrong, who drove on towards the Motherwell goal before dispatching his shot into the top corner to virtually make the points safe.

Soon after, Ciftci almost had his hat-trick, but Nielsen got a hand to the shot to divert it on to the post.

United's fourth came soon after as a fantastic long pass from Gavin Gunning found Dow unmarked in the box and his finish into the corner was perfect as United put Motherwell to the sword.

Another United attack then tore Motherwell apart through the middle, presenting substitute Graham with the chance and the striker calmly slotted it home.

United kept pressing for more goals, but it was Motherwell who found the net next when Ainsworth's shot rifled in from the edge of the box.